A clutch apparatus for a transporting machine comprises a wet-type multiplate clutch structure. The wet-type multiplate clutch structure comprises a cylindrical clutch drum having a bottom. In the clutch drum, driven plates and a piston are provided so as to be movable in the axial direction, and a ring-shaped coned disc spring is provided between the driven plate, which is proximate to a bottom surface of the clutch drum, and the piston (for example, see the following patent document 1). The coned disc spring is disposed such that an inner side surface thereof is supported by the piston and an outer side surface thereof is supported by the driven plate proximate to the bottom surface. The coned disc spring is elastically deformed from the dish shape into an approximately flattened shape, thereby absorbing shocks occurring during the engagement of the clutch of the clutch structure.
In such a coned disc spring, when the coned disc spring is deformed into an approximately flattened shape by elastic deformation, the displacement amount of the coned disc spring reaches the stroke length ST defined by the difference of the height H and the thickness T as shown in FIG. 10. At this time, a load is generated in the coned disc spring (hereinafter called “load in a flat condition”), and the load may be a design parameter for the clutch structure. The load in a flat condition depends on the outer diameter, the inner diameter, the thickness T, and the stroke length ST of a coned disc spring. The outer diameter, the inner diameter, and the stroke length ST of a coned disc spring are preselected as design parameters for a clutch structure. Therefore, the load in a flat condition is controlled by the thickness T.    The patent document 1 is Japanese Unexamined Patent Application Publication No. 9-032918.
Clutch apparatuses of automobiles having CVT (Continuously Variable Transmission) or AT (Automatic Transmission) may comprise plural clutch structures that have the same axis line and differ in size with respect to each other. Each clutch structure is provided with a coned disc spring having an outer diameter corresponding to the clutch drum thereof. In this case, since loads in flat conditions of the coned disc springs are not generally the same, the respective coned disc springs are made from materials having different thicknesses.
After a blank of a coned disc spring is punched from a sheet of material, the rest of the sheet of material cannot be used and may be scrapped. Therefore, large amounts of sheet of material are scrapped in the above-mentioned production of the coned disc spring. Accordingly, the material yield of the coned disc spring is low, thereby increasing the production cost.